Address failing tests from ethereum/tests v11.1

- Difficulty calculation was taking into account the parent ``difficulty`` which would slip below the ``DIFFICULTY_MINIMUM`` value if the parent ``difficulty`` was less than the allowed minimum. Instead, just take the max between the difficulty calculation and the actual minimum.

eth/vm/forks/byzantium/headers.py

@@ -60,7 +60,7 @@ def compute_difficulty(
     )
     difficulty = max(
         parent_difficulty + offset * adj_factor,
-        min(parent_header.difficulty, DIFFICULTY_MINIMUM)
+        DIFFICULTY_MINIMUM
     )
     num_bomb_periods = (
         max(

eth/vm/forks/homestead/headers.py

@@ -46,13 +46,16 @@ def compute_homestead_difficulty(parent_header: BlockHeaderAPI, timestamp: int)
     offset = parent_header.difficulty // DIFFICULTY_ADJUSTMENT_DENOMINATOR
     sign = max(
         1 - (timestamp - parent_tstamp) // HOMESTEAD_DIFFICULTY_ADJUSTMENT_CUTOFF,
-        -99)
-    difficulty = int(max(
+        -99,
+    )
+    difficulty = max(
         parent_header.difficulty + offset * sign,
-        min(parent_header.difficulty, DIFFICULTY_MINIMUM)))
+        DIFFICULTY_MINIMUM
+    )
     num_bomb_periods = (
         (parent_header.block_number + 1) // BOMB_EXPONENTIAL_PERIOD
     ) - BOMB_EXPONENTIAL_FREE_PERIODS
+
     if num_bomb_periods >= 0:
         return max(difficulty + 2**num_bomb_periods, DIFFICULTY_MINIMUM)
     else:

newsfragments/2084.bugfix.rst

@@ -0,0 +1 @@
+Use the ``DIFFICULTY_MINIMUM`` more appropriately as the lower limit in all difficulty calculations.

tests/core/consensus/test_pow_mining.py

@@ -77,7 +77,7 @@ class ChainClass(MiningChain):
 
     chain = genesis(ChainClass)
 
-    block = chain.mine_block()
+    block = chain.mine_block(difficulty=1)
     check_pow(
         block.number,
         block.header.mining_hash,

tests/json-fixtures/blockchain/test_blockchain.py

@@ -317,15 +317,6 @@ def blockchain_fixture_mark_fn(fixture_path, fixture_name, fixture_fork):
         return pytest.mark.skip(
             "EIP-2681 update not implemented. HighNonce tests turned off for now."
         )
-    elif any(_ in fixture_name for _ in (
-            "CreateAddressWarmAfterFailureEF", "doubleSelfdestructTouch",
-            "delegatecall09Undefined_d0g0v0", "senderBalance_d0g0v0",
-            "touchAndGo_d0g0v0",
-    )):
-        return pytest.mark.skip(
-            "Skipped failing tests in v11.1 update to get Merge-related changes in. "
-            "Turn these back on and fix after the Merge is implemented."
-        )
     elif "Merge" in fixture_name:
         # TODO: Implement changes for the Merge and turn these tests on
         return pytest.mark.skip("The Merge has not yet been implemented.")